A Retrospective Analysis of the Immunotoxicity Study - US EPA

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

MEMORANDUM

Date: February, 2013

SUBJECT: A Retrospective Analysis of the Immunotoxicity Study (OCSPP Test Guideline No. 870.7800)

PC Code: NA Decision No.: NA Petition No.: NA Risk Assessment Type: NA TXRNo.: NA MRIDNo.: NA

DP Barcode: NA Registration No.: NA Regulatory Action: NA Case No.: NA CAS No.: NA 40CFR: NA

FROM:

Jess Rowland le..s.s. (C....u.. ~""'-"--

Associate Director Health Effects Division

Ver.Apr. 20 l 0

TO:

Jack Housenger,

Director

Health Effects Division

In 2011, CropLife America (CLA) conducted a retrospective evaluation of 82 irnmunotoxicity studies to determine the potential regulatory impact of this study. The assessment concluded that the large majority of studies demonstrated no treatment-related effects at the high dose level for the given study and in no case was the irnmunotoxicity finding the most sensitive endpoint when compared to other existing toxicity endpoints in the data base, indicating the lack of impact ofthese studies on human health risk assessments. Based on their findings, the CLA requested that the Agency begin granting waivers for the irnmunotoxicity guideline study based on its authority under 40 CFR ? 158.45 to grant waivers for studies for which "the data would not be useful in the Agency's evaluation of the risks or benefits of the product."

In 2012, the Office of Pesticide Programs (OPP) similarly conducted a retrospective analysis of over 170 irnmunotoxicity studies (including the 82 chemicals evaluated by CLA) for the purpose of 1) assessing if the results of the guideline immunotoxicity study impact human health risk assessment; 2) determining whether there is sufficient justification for granting waivers for this immunotoxicity study; and 3) proposing a path forward. The results of this analysis are presented in this document.

A Retrospective Analysis of Immunotoxicity Studies (870.7800)

Health Effects Division Office of Pesticide Programs U.S Environmental Protection Agency

February,2013

Health Effects Division Office of Pesticide Programs U.S. Environmental Protection Agency

I. INTRODUCTION

In 2007 the 40 CFR Part 158 Toxicology Data requirements were revised to include an immunotoxicity study (870.7800). This study provides an evaluation of the function of immune systems components (i.e., humoral or cell-mediated type immunity) which allow a better characterization of potential immunotoxicity for a test chemical.

The Office of Pesticide Programs (OPP) has now received and reviewed over 170 of these studies. Given that large number of these new immunotoxicity studies have now been submitted, OPP believes it is appropriate to conduct retrospective analysis for the purpose of 1) assessing if the results of the guideline immunotoxicity study impact human health risk assessment; 2) determining whether there is sufficient justification for granting waivers for this immunotoxicity study; and 3) proposing a path forward.

II. BACKGROUND

1. Toxicity Testing in General

OPP routinely requires extensive toxicity testing that evaluate a wide range of toxic effects for conventional pesticides as stipulated in 40 CFR Part ?158 Toxicology Data requirements. These studies provide the scientific basis for characterizing the potential hazard of pesticide exposure. Toxicity studies are conducted in multiple species (mice, rats, rabbits, and dogs) for various durations (acute, subchronic and chronic) and evaluate various endpoints (nervous system, developmental-, reproduction, subchronic and chronic toxicity, immunotoxicity, carcinogenicity and mutagenicity). The Agency uses these studies to examine whether adverse effects are caused by different durations of pesticide exposure ranging from short-term (acute) to long-term (chronic) exposure and different routes of exposure (oral, dermal, or inhalation).

Toxicity studies allow the Agency to determine the level of exposure to the pesticide at which adverse effects might occur. An important aspect of this determination is assessing the relationship between exposure (dose) and response (often referred to as the dose-response analysis). The Agency then chooses values from a dose-response curve at the low end of the observable data (i.e., the no observed adverse effect level, NOAEL and the lowest-observed adverse effect level, LOAEL, or a modeled benchmark dose) as a starting point for conducting a quantitative risk assessment. These values are referred to as the Points of Departure (POD). Separate PODs may be established for dietary (acute and chronic) and non-dietary pathways (incidental oral, dermal and inhalation) for various durations of exposure (short, intermediate and long term).

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2. Immunotoxicity Testing in General

The immune system is responsible for modulating host defenses against a range of human diseases. The successful development and functioning of the immune system require recognition and response to a range of cellular and circulating signals acting by endocrine, autocrine, and paracrine mechanisms. These complex control systems offer multiple opportunities for disruption by environmental chemicals such as agricultural pesticides.

In 1993, the National Research Council (NRC) concluded that an analysis of the impact or toxicity of agricultural chemicals on the immune system is essential. Finding that there is a paucity of information on the effects of many chemicals on the developing and indeed on the mature immune system, the NRC recommended development of a battery of consensus tests to protect the developing immune system (NRC, 1993).

In 1996, the Agency's Science Advisory Panel (SAP) reviewed the draft guidelines for the immunotoxicity testing (OPPTS 870.7800) and agreed that the immune system is a legitimate target organ for toxicity. The SAP concluded that the OPP's proposed methodology was sufficiently validated in both the rat and mouse systems for inclusion into routine toxicology hazard evaluation studies. (SAP, 1996).

The European Union (EU) includes functional immunotoxicity testing assessment of the immune system in its 90-day rodent study and not as a core requirement. The Organization of Economic Co-operation and Development (OECD) make use of the Extended One-Generation Reproduction Study (OECD Test Guideline 443) to assess the potential impact of chemical exposure on the developing immune system in lieu of a guideline study.

3. EPA's Functional Immunotoxicity Study

Traditional subchronic and chronic rodent studies can provide some information on certain immunological endpoints such as hematology, lymphoid organ weights and histopathology. Nonetheless, EPA concluded in 2007 that these endpoints alone do not provide a full and integrated evaluation of immune function. Evaluating the potential of a chemical to adversely affect the immune system function is important because immune system suppression has been associated with increased incidences of diseases. Accordingly, that year the Agency revised the Part 158 Toxicology Data requirements to require a functional immunotoxicity study for all food and non-food use pesticides.

The Agency's immunotoxicity study (OPPTS. 870.7800) is designed to evaluate the immunosuppressive potential of a chemical by measuring antibody production to sheep red blood cells (SRBCs), aT-dependent antigen, in mice or rats. The T-cell dependent antibody response (TDAR) is dependent on functional T-cells, B-cells and antigen processing/presenting cells and is considered a reliable indicator for measuring humoral immune function (USEPA, 2008, 2009).

In the immunotoxicity study, mice and/or rats are exposed orally (gavage or diet) or via inhalation to the test and control substances for at least 28 days. Four or 5 days prior to the end of exposure (e.g., day 24 or 23 of the study) animals are immunized by intravenous or intraperitoneal injection of SRBCs. The day of immunization depends on whether antibody

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forming cells (day 23) or antibody titers (day 24) are assessed. Animals are sacrificed on Day 29. At the end of the exposure period, either the plaque forming cell assay (PFCA) or an enzyme linked immunosorbent assay (ELISA) is performed to determine TDAR through evaluation of the effects on the number of splenic anti-SRBC producing cells or serum antiSRBC IgM titers, respectively. Other parameters evaluated in the study include mortality, clinical signs of toxicity, body weight, body weight gain, food consumption, water consumption, organ weights (i.e. spleen and thymus), and macroscopic pathology.

Depending on the outcome of the anti-SRBC assay, it may be necessary to perform a quantitative analysis of the effects of a chemical on the numbers of cells in major lymphocyte populations and T cell subpopulations by flow cytometry, or a splenic NK cell activity assay to assess the effects of the test compound on non-specific (innate) immunity

4. Non-EPA Retrospective Analysis

CropLife America conducted a retrospective evaluation of 82 TDAR studies to determine the potential regulatory impact of the immunotoxicity study. The assessment concluded that the large majority of studies demonstrated no treatment-related effects on TDAR at the high dose level for the given study. A reduction in TDAR was observed in 4 of the 82 studies at the highdose level only; however, in no case was the immunotoxicity finding the most sensitive endpoint when compared to other existing toxicity endpoints in the data base, indicating the lack of impact of these studies on human health risk assessments (CLA, 2011, 2012).

OPP is now in position to complete a more comprehensive retrospective than the industry evaluation.

II. METHODS

A. Studies Evaluated: The data set included 171 immunotoxicity studies

conducted on 155 chemicals representing a range of product types and chemical structures

including older and newer active ingredients. HED conducted an independent review of the studies and prepared Data Evaluation Records (DERs). The DER is the official record of

independent review with sufficient detail to support study conclusions and contains the data

review and analysis of study results. Only guideline acceptable studies were considered in th"IS anaLlySI.S.

Total

Rat

Mouse Both Species

Number of Chemicals Tested 155

83

58

14

Number of Studies Conducted Total

Rats

97

Mice

74

* Two chemicals were evaluated in more than one study

Males 30 12

Females 40 51*

Both Sexes 27 11

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